Effects of light cycle on motion behaviour and melatonin secretion in Haliotis discus hannai

Abstract

The abalone Haliotis discus hannai is a typical nocturnal marine invertebrate. In this study, a quantitative analysis was performed on the motion behaviour characteristics of abalones exposed to different light cycles (0 L:24D, 12 L:12D, 24 L:0D) using infrared camera and behavioural analysis software. A preliminary analysis of the intrinsic correlations between melatonin secretion and abalone behaviour rhythms was also conducted. The results showed that the cumulative moving distance and duration of movement for abalone in the 0 L:24D group were significantly higher than those in the 12 L:12D and 24 L:0D groups (P < 0.05). The mean and maximum moving velocities of abalones in the 12 L:12D group were significantly higher than those in the 0 L:24D group (P < 0.05). The maximum cumulative moving distance and duration of movement for abalone in the 12 L:12D and 24 L:0D groups occurred between 00:00–03:00. In the 0 L:24D group, peak cumulative moving distance and duration movement were recorded between 00:00–03:00 and 15:00–18:00. According to the results of cosine analysis, melatonin content and expression levels of aralkylamine N-acetyl transferase (AANAT) and N-acetylserotonin O-methyltransferase (ASMT) in the 12 L:12D and 24 L:0D groups showed significant circadian cosine rhythms (P < 0.05) and tended to be higher during the day and lower at night. Compared with the variation trend of melatonin, the expression levels of melatonin receptor (MTR) in each group showed significant circadian cosine rhythms (P < 0.05). Especially in the 0 L:24D group, the expression levels of MTR also tended to be higher during the day and lower at night, indicating that MTR may mediate other factors which participate in the regulation of abalone circadian rhythms. The results of this study provide a quantitative description of the motion behaviour characteristics of abalone exposed to different light cycles. The intrinsic correlation between melatonin secretion and abalone motion behaviour rhythms was also examined in this study, which in turn provides a reference for light regulation and feeding strategies in aquaculture production.